Ignition device for rocket motors

ABSTRACT

An ignition device for igniting a rocket motor comprising a striker adapted for displacement by pressure generated by the auxiliary charge, a percussion-operated priming device for impact by the striker, and an ignition charge for ignition by the priming device and for igniting the rocket motor.

United States Patent Trapp Sept. 5, 1972 [54] IGNITION DEVICE FOR ROCKET 2,773,448 12/1956 Jasse ..l02/49.7 MOTORS 3,176,615 4/1965 De Matthew ..l02/49.7 72 Inventor; A h Hubert Trapp, 3,204,559 9/ 1965 D6 Matthew ..l02/49.7 dermmste" England FOREIGN PATENTS 0R APPLICATIONS [73] Assgnee' ax-g 5: 2: 14,000 1896 Great Britain 102/491 [22] Filed: 1970 Primary Examiner-Verlin R. Pendegrass [21] Appl, No,; 79,770 Attorney-Cushman, Darby & Cushman [30} Foreign Application Priority Data [57] ABSTRACT An ignition device for igniting a rocket motor com- 1969 Great Bmam "52768/69 prising a striker adapted for displacement by pressure [52 us. Cl .1 ..102/49.7 generated by the auxiliary charge a Percussim' 51 Int. Cl. ..F42c 1910s Operated Priming device for impact by the Striker, and [58] Field of Search ..102/49.7 an ignition charge for ignition y the Priming device and for igniting the rocket motor. [56] References Cited 1 Claim, 3 Dm Figures UNITED STATES PATENTS 2,701,525 2/1955 Hickman l02/49.7

l4 ll 5Q 2513 24 6O 56 SI l7 29 58 IS lb 1 IGNITION DEVICE FOR ROCKET MOTORS BACKGROUND OF THE INVENTION This invention relates to ignition devices for rocket motors, and is more particularly concerned with an ignition device for the rocket motor of a missile of the type which is launched from a tube by an auxiliary charge, for example from a field or naval gun. This type of missile will be referred to in this specification as a rocket-assisted shell.

Rocket-assisted shells are well-known, and generally operate on the basis of the shell being launched by an auxiliary charge to provide initial momentum, followed by a boost in momentum provided by a rocket motor built into or attached to the shell. The rocket motor has to be ignited by some device, and it is with this ignition device that the invention is concerned.

It has been proposed for the operation of the ignition device to be initiated electrically, initiation being either instantaneous with, or delayed until after, firing the auxiliary charge. This proposal can be unsatisfactory in that electrical initiation is susceptible to interference by radar systems, leading to the possibility of pre-ignition occuring' either accidentally or deliberately by enemy agency. In addition the use of delayed electrical initiation necessitates the provision of an electrical supply in the shell, thereby producing weight and space problems.

It has also been proposed for the operation of the ignition device to be initiated by a mechanical system, for example by a clockwork device or the triggering of a spring-loaded plunger. Such mechanical systems, however, rely upon energy stored mechanically in the shell, for example in the springs of the clockwork device or the spring of the spring-loaded plunger. Thus, these mechanical systems tend to be bulky and involve weight problems, and the inherent moving parts can stick or jam with only limited stored energy available to cause them to function. As well as weight and space problems, reliability is questionable.

It is an object of the present invention to provide an ignition device for a rocket-assisted shell which reduces weight and space problems and improves the reliability of operation.

SUMMARY OF THE INVENTION According to one aspect of the present invention, an ignition device for igniting the rocket motor of a rocket-assisted shell as hereinbefore referred to, comprises a striker adapted for displacement by pressure generated by the auxiliary charge, a percussionoperated priming device for impact by the striker, and an ignition charge for ignition by the priming device and for igniting the rocket motor.

The striker may be slidably movable within a container body of the device and retained in the inoperative position by one or more frangible elements.

The frangible element may be a shear pin, washer or disc for example, which is disposed forwardly of the striker and within the container body, or the frangible element may constitute a key to mechanically key together the body and the striker. Instead of providing separate frangible elements, the body or striker may have a frangible element formed integrally therewith. Such an integrally formed frangible element may, for example, be an annular rim provided on the body or the striker.

Pre-tensioning means such as a spring for example may be provided rearwardly of the striker to assist its forward movement upon breaking of the frangible element.

Preferably, a fluid-tight seal is provided between the body and the striker to prevent gases from the auxiliary charge permeating to the front of the striker.

As an alternative to the sliding arrangement of striker, a striker may take the form of a concavo/convex disc located transversely of the container body so that in the inoperative condition of the ignition device, the concave side of the disc faces the priming device and upon actuation of the device by an auxiliary charge, the pressure of this charge applied to the convex side of the disc is sufficiently great to reverse the curvature of the disc and cause the center of the disc to snap through a plane containing the periphery of the disc and effect impact of the striker with the priming device.

The percussion-operated priming device is conveniently of a type employed in the construction of shotgun-cartridges and comprises a cap chamber containing a priming (fulminating) composition and an anvil.

A time delay fuse element may be interposed between the priming device and the ignition charge to delay the firing of the rocket motor until the motor has achieved a safe distance from the launching position.

According to a second aspect of the invention, a rocket-assisted shell as hereinbefore referred to comprises an ignition device in accordance with the abovedescribed first aspect, said device being ejectably retained in the exhaust nozzle of the exhaust nozzle of the rocket motor by mounting means which comprises at least one frangible element, the device being ejectable from the nozzle by pressure of the exhaust gases emanating from the rocket motor.

Conveniently, the ignition device may be ejectably retained in the exhaust nozzle of the rocket motor by an annular nut screw-threadably engaged at one end with the rocket motor and having adjacent the other end a radially inwardly directed flange engageable with a rearwardly facing surface of the ignition device, the flange being shearable from the remainder of the nut by pressure of the exhaust gases from the rocket motor.

The flange may be formed integrally with the remainder of the nut, or the flange may comprise a separate annular ring secured to the nut at a frangible connection.

DESCRIPTION OF THE DRAWINGS Two embodiments of the invention will now be more particularly described by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is an axial cross-section of the rear end portion of a rocket motor and shows a first embodiment of an ignition device mounted in the exhaust nozzle;

FIG. 2 is an axial cross-section on a larger scale showing the ignition device of FIG. 1; and

FIG. 3 is a view similar to part of FIG. 2 but showing a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1, numeral 10 denotes generally the rear portion of a rocket motor comprising an end ring 11 screw-threadably engaged in the rear end of a tubular rocket motor casing 12, and having a rearwardly projecting neck portion 12a externally screw-threaded as at 13 for a purpose to be described later in the specification. The ring 11 has a liner 14 of an asbestos based composition. The rear portions of the ring 14 and its liner are stepped as at 15 to provide a location for a graphite insert ring 16, the liner and insert ring being shaped to constitute an exhaust nozzle 17 of conventional configuration.

Forwardly of the end ring 11 and its liner 14 the casing 12 envelops an annular series of castable fuel elements 18. Intermediate the graphite ring 16 and the fuel elements 18 a perforated aluminum container 19 of which the holes are covered by aluminum foil holds a boost ignition charge 20. Within the container 19 are aluminum struts 21 which serve to support a diaphragm 22 separating the fuel elements 18 from the remainder of the contents of the rocket-assisted shell of which the rocket motor is an integral part.

An ignition device of the first embodiment is denoted generally by numeral 24 and is ejectably retained in the exhaust nozzle 17 by mounting means comprising an annular nut 25 engaged on the screw thread 13.

Turning now to FIG. 2, the ignition device 24 comprises a hollow container body 26 having a frusto-conical forward end portion 27 to suit the taper of the divergent end of the exhaust nozzle 17. The portion 27 is circumferentially grooved at 28 to receive an O-ring seal and thereby provide a fluid-tight seal between the end portion 27 and the nozzle. Rearwardly of the end portion 27 a circumferential flange 29 is provided rearwardly of which the remaining length of the body is cylindrical.

The body 26 is axially bored to provide, commencing with the rearward end, a chamber 30 of which the inner end has a screw-threaded recess 31, this recess reducing to a cavity 32. The cavity is separated from a chamber 33 of slightly larger diameter by a flange 34. Near the forward end of the body, the chamber 33 opens into a screw-threaded recess 35.

At the base of the chamber 33, the flange 34 provides a seat for an O-ring seal 36 disposed between the flange and a time delay fuse element 37 which is slidably engaged within the chamber 33. For a 2.5 second delay, a typical delay composition is 36 percent by weight antimony powder and 64 percent by weight potassium permanganate. For shorter delays, for example down to 0.020 second, a lead dioxide/silicon compound can be used.

The forward end of the fuse element 37 projects slightly from the chamber 33 so that a retaining ring 40 screw-threadably engaged in the recess 35 retains the fuse axially of the body and against the seal 36. The bore of the ring 40 and the recess 35 contain a black powder ignition charge 41 (typically 0.25 gm) which is retained by a thin frangible disc 42 of annealed aluminum and an end ring 43.

Within the cavity 32, there is received a percussionoperated priming device 45. This priming device comprises a cap 46 containing, adjacent its base, a priming powder 47 of the following composition by weight:

Barium styphnate Potassium chlorate 48% Antimony sulphide 32% Lead dinotroresorcinate 5% Tetrazene 5% In the present embodiment a total weight of priming powder of 0.02 gm was employed.

The cap 46 also contains an anvil 48 frictionally held within the cap. The constructionof the priming device, apart from the above powder composition, is of conventional design as used in the manufacture of shotgun cartridges.

The priming device is held in the cavity 32 by a ring 49 screwed into the recess 31.

A striker 51 comprises a cylindrical portion 52 slidably engaged within the chamber 30, and a percussion element in the form of an axial projection 53 at the forward end suitably dimensioned to pass through the ring 49 and to contact the priming device 45. The cylindrical portion 52 of the striker is circumferentially grooved to receive an O-ring seal 54 so as to provide a fluid-tight seal between the striker and the wall of the chamber 30.

In the inoperative condition of the ignition device, the striker 51 is positioned in the chamber 30 so that the projection 53 is spaced a distance from the ring 49 and the striker is mechanically keyed to the body 26 in this position by means of a frangible element in the form of a shear pin 55 of relatively small diameter (in the present embodiment one-sixteenth inch (l.6mm)) and extending diametrically through the striker and into opposed radial holes in the container body 26 as shown in FIG. 2.

Reverting to FIG. 1 of the drawings, the annular nut 25 comprises an internally screw-threaded portion 56 for engagement on the screw-thread 13 of the rocket motor. An internal flange 57 of the nut has an inner diameter slightly greater than that of the flange 29 of the body 26, and provides a recess 58 for location therein of a ring 59. This ring has a radial thickness such that it extends radially inwardly of the flange 57. The ring 59 is retained in the recess 58 by means of frangible elements in the form of six shear pins 60 equiangularly spaced around the nut 25 and extending radially through the nut and the ring. 4 In use, the ignition device 24 is fitted with, say, a 2.5 second delay fuse and is located in the exhaust nozzle of a rocket motor of a rocket-assisted shell, the device 24 being held in position by the annular nut 25 and the ring 59 as shown in FIG. 1.

Upon launching the rocket-assisted shell from a barrel by means of an auxiliary launching charge (not shown), a pressure of typically 4,000 p.s.i. (2.8 kglmm generated by the charge is exerted against the rear face of the striker 51 which, because of its lower mass per unit of area of the rear face than that of the whole shell, is forced forwards relatively to the body 26 thereby shearing the pin 55. The striker then moves forward within the body 26 and the projection 53 moves through the ring 49 to impact against the priming device 45. This impact detonates the priming composition 47 which initiates the time delay fuse element 37. Following the pre-arranged time delay of 2.5 seconds the ignition charge 41 of black powder ignites and bursts the aluminum disc 42 whereupon the heat generated ignites the further boost ignition charge 20 and this, in turn, ignites the castable fuel elements 18 forming the self-propelling charge of the rocket motor. The resultant exhaust gases emitted through the nozzle l7 build up and press the ignition device 24 against the ring 59 in the nut 25; At approximately half the mag.-

n'itude of the eventual exhaust gas pressure to be developed by the rocket motor, the shear pins 60 are designed to fracture whereupon the ignition device is.

ejected from the nozzle.

An ignition device of the second embodiment and of which the rearward part only is shown in FIG. 3, is

generally similar to'the device of the first embodiment. However, in this second embodiment, a striker 61 comprises a concavo/convex disc 62 made of spring materithe disc moves the projection 63 through the ring 68 to tainer body 66. In the inoperative condition of the ignition device the concave side of the disc faces a priming device 67 and ring 68.

In use, the pressure generated by an auxiliary launching charge (not shown) applied to the convex side of the disc reverses the curvature of the disc and causes the center of the disc to snap through a plane containing the periphery of the disc. This snap action of impact into the priming device 67.

I claim:

1. A rocket-assisted shell to be launched from a tube by an auxiliary charge, the shell comprising a rocket motor having an exhaust nozzle and an ignition device ejectably retained in said exhaust nozzle, the devicecomprising a hollow body having an external flange cooperable with an internal flange of a nut whereby the body is connectable to the associated shell, said internal flange 'of the nut being shearable from the remainder of the nut by pressure of the exhaust gases,- said body further comprising an axial bore'containing in succession from its rearward end, a striker fluid tightly slidable along the bore, a percussion-operated priming device'for impact by the' striker, a time delay fuse element, and an ignition charge for igniting the rocket motor of the associated shell, the striker being retained in the inoperative position by a frangible shear pin which mechanically keys together the body and the striker, whereby upon firing the shear pin is fractured to permit the striker to impact with the priming device. 

1. A rocket-assisted shell to be launched from a tube by an auxiliary charge, the shell comprising a rocket motor having an exhaust nozzle and an ignition device ejectably retained in said exhaust nozzle, the device comprising a hollow body having an external flange cooperable with an internal flange of a nut whereby the body is connectable to the associated shell, said internal flange of the nut being shearable from the remainder of the nut by pressure of the exhaust gases, said body further comprising an axial bore containing in succession from its rearward end, a striker fluid tightly slidable along the bore, a percussion-operated priming device for impact by the striker, a time delay fuse element, and an ignition charge for igniting the rocket motor of the associated shell, the striker being retained in the inoperative position by a frangible shear pin which mechanically keys together the body and the striker, whereby upon firing the shear pin is fractured to permit the striker to impact with the priming device. 